<template>
  <ul class="list">
     <li class="item"
        v-for="item of letters"
        :key="item"
        :ref="item"
        @click="handelClick"
        @touchstart="handelTouchStart"
        @touchmove="handelTouchMove"
        @touchend="handelTouchEnd"
        >{{item}}
     </li>
  </ul>
</template>

<script>
export default {
  name: "CityAlphabet",
  props:{
    cities:Object
  },
  computed: {
    letters (){
      const letters = [];
      for (let i in this.cities){
        letters.push(i)
      }
      return letters;
    }
  },
  data (){
    return {
      touchStatus:false,
      startY:0,
      timer:null
    }
  },
  updated (){
    this.startY = this.$refs['A'][0].offsetTop;
  },
  methods:{
    handelClick (e){
      //console.log(e.target.innerText);
      this.$emit('change',e.target.innerText);
    },
    handelTouchStart (){
        this.touchStatus = true;
    },
    handelTouchMove (e){
         if(this.touchStatus){
            if(this.timer){
                clearTimeout(this.timer)
            }
            this.timer = setTimeout(() => {
                const touchY = e.touches[0].clientY - 79;
                const index = Math.floor((touchY-this.startY) / 20);
                if(index >=0 && index < this.letters.length){
                    this.$emit('change',this.letters[index]);
                }
            },16)
        }
    },
    handelTouchEnd (){
       this.touchStatus = false;
    }
  }
};
</script>

<style scoped lang="stylus">
@import '~styles/varibles.styl';

.list {
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: absolute;
  top: 1.58rem;
  right: 0;
  bottom: 0;
  width: 0.4rem;

  .item {
    line-height: 0.4rem;
    text-align: center;
    color: $bgColor;
  }
}
</style>
